The invention relates to a simulator apparatus with at least two degrees of freedom of movement for an instrument that has an elongated shaft, comprising a holding device for the instrument, the holding device being designed such that the instrument has at least a first degree of freedom of rotary movement about a longitudinal axis of the shaft and at least a second degree of freedom of translatory movement in the direction of the shaft, the holding device having a gear arrangement for the first and second degrees of freedom.
Such a simulator apparatus is known from EP-A-0 970 662.
In general, such a simulator apparatus is used as interface between an operator and an instrument in simulators. A specific use, to which the following description relates without limiting the present invention thereto, is the integration of a simulator apparatus mentioned at the beginning in a simulator for simulating a minimally invasive surgical intervention in a human or animal body.
The term xe2x80x9cinstrumentxe2x80x9d is to be understood generally in the sense of the present invention, and in the case of a medical simulation, it can be an endoscope, a tool such as scissors, forceps, a dissector, clamp applicator etc.
In recent years, minimally invasive surgery has gained clearly in importance by comparison with open surgery. In minimally invasive surgery, a viewing system, for example an endoscope, and one or more instruments such as forceps, scissors, HF instruments, clamp applicators, etc. are introduced into the body by minimal incisions. The minimally invasive surgical operation is carried out with video assistance with the aid of the abovementioned instruments in combination with peripheral devices.
At present, minimally invasive surgery is used, for example, for removing a gall bladder, the appendix and for handling herniotomies. Further fields of use are being opened up.
However, xe2x80x9cminimally invasivexe2x80x9d surgery covers as a term not only surgical interventions, but also interventions such as, for example, the introduction of substances into the body, or biopsies where use is made of the minimally invasive technique.
By contrast with open surgery, the advantage of the minimally invasive technique resides in the mode of procedure, which spares the patient and entails less surgical trauma, shorter times of stay in hospitals and a shorter incapability for work.
By contrast with open surgery, however, the handling of the instruments during a surgical intervention is substantially more complicated, firstly because the freedom of movement of the instrument inserted through the incision is restricted because of the only small incision, and secondly because the surgeon does not himself have a clear dimensional view of the working tip of the instrument located in the body, nor of the operating site, but instead only a two-dimensional visual monitoring is possible via the video monitor. It goes without saying that the coordination of the guidance and operation of the instrument or instruments are thereby rendered more difficult.
There is thus a greater need for training in the new techniques of minimally invasive surgery. Various alternatives currently exist for training in surgical procedures of minimally invasive surgery.
One alternative consists in carrying out training operations in vivo on animals, specifically on pigs. However, such training is cost intensive, time consuming to prepare and, moreover, ethically dubious.
In the case of a further alternative, physicians are trained on in vitro organs in a training box into which the instruments can be appropriately introduced. The organs arranged in the training box are certainly biological organs, but training in the case of this alternative is likewise time consuming to prepare and cannot be regarded as realistic.
Finally, training in minimal invasive surgery is currently being carried out on model organs or training objects in a training box. However, such model organs are not sufficiently realistic for training for an entire operation. Moreover, the preparation of the model organs and training objects requires a not inconsiderable preparatory outlay, since the models are for the most part destroyed during the operation and initially require to be prepared again for further training sessions.
Because of the disadvantages of the training systems used to date, there was already a need very early for so called virtual simulators that can be used to overcome the disadvantages of the previous training systems.
The actual operating site is generated exclusively via a computer in the case of virtual simulation. Realistic simulation requires a model database that fixes the geometric shapes and physical properties of the tissues, organs and vessels, as well as the geometry and kinematics of the instrument or instruments. In the journal xe2x80x9cBiomedical Journalxe2x80x9d, Volume No. 51, April 1998, U. Kxc3xchnapfel describes a xe2x80x9cVirtual-Reality-Trainingssystem fxc3xcr die Laparoskopiexe2x80x9d [xe2x80x9cVirtual reality laparoscopy training systemxe2x80x9d] that has an input box which exhibits from the outside the customary instrument grips and a virtual endoscope. In the housing, the minimally invasive instruments are guided in a mechanical guide system that further permits the detection of the deflection of the instruments and actuators. In addition, various foot switches are present that can be used to activate surgical and general functions. Via angle encoders, for example, a PC-based sensor data acquisition process measures the positions of the joints of the operating instruments and transmits these continuously to a graphics workstation. A xe2x80x9cvirtualxe2x80x9d image of the endoscope view is calculated there from in real time. The consistency of the tissue to be treated is fed back to the operator realistically as force feedback by inherently calculated xe2x80x9cvirtualxe2x80x9d reactive forces between organs and instruments.
Consequently, in the case of virtual simulation of minimally invasive interventions, no use is made of physically present organsxe2x80x94instead the spatial and physiological structures of such organs are present as data in a computer. The simulator apparatus mentioned at the beginning in this case forms the interface between the operator and the instrument to be handled and the simulation computer system. The operator to be trained handles the instrument accommodated in the mechatronic simulator apparatus, the data stored in the computer, for the spatial and physiological structure of the virtual organ being transmitted as force feedback by the simulator apparatus to the instrument while the latter is being handled, as a result of which the operator is afforded a realistic feel.
The previous developments in this field have concentrated primarily on the creation of the simulation software, while so far available holding systems capable of localization have been used as mechatronic simulator apparatus. In the interests of realistic simulation, the simulator apparatus should take account of all degrees of freedom that are present for a minimally invasive surgical instrument, specifically a tilting of the instrument about the surface of the body, a movement in the direction of the shaft and a rotary movement about the longitudinal axis of the shaft. However, a problem in this is the mechanical implementation of these many degrees of freedom in the holding device of the simulator apparatus for the instrument.
For example, the simulator apparatus known from U.S. Pat. No. 6,024,576 comprises a complicated mechanical lever system whose disadvantage resides particularly in the fact that the simulator apparatus is very large overall. It is therefore impossible using such a simulator apparatus for two or more apparatuses to bring a plurality of instruments so close together that the instrument tips can touch. Because of the many levers used in this known simulator apparatus, undesirable moments of inertia and torques occur when this simulator apparatus is being used and must be compensated in a complicated way in order to permit a realistic force feedback.
The simulator apparatus known from EP-A-0 970 662 mentioned at the beginning is used in a surgical simulator system that simulates the placing of a catheter into blood vessels. This known simulator system ensures a haptic force feedback to the user of a set of catheters or similar tubular objects that are coupled to the system. An actuator arrangement is coupled to the objects and likewise to a computer station that carries out a surgical procedure with the aid of a simulation program. The actuator arrangement has a set of mutually spaced actuators, each actuator being coupled mechanically to a corresponding object by means of a rigid tube that is used as an extension of the object inside the actuator arrangement. Each actuator of the arrangement comprises sensors generating signals that indicate an axial translatory movement and a rotary movement of the object by the user. The signals detected are transmitted to the computer. The computer calculates as a response to these signals axial forces and torques that must be exerted on the object as haptic force feedback, and generates drive signals for the actuator arrangement. Each of the actuators has a gear arrangement that is connected via supports and holders to the rigid tube or to the simulating catheter. However, the configuration of this gear arrangement disadvantageously leads to a higher moment of inertia for the actuator itself. This has the disadvantage that the user of the simulator apparatus already senses a force feedback because of the high moments of inertia of the actuator even when this feedback does not normally occur for the purpose of the catheter movement being simulated. Again, the known actuators have a very large overall size.
Furthermore, WO 96/30885 discloses a virtual surgery system that makes use as input apparatus of a mouse, a joystick, a three-dimensional mouse or a seven-dimensional joystick. The disadvantage with this type of simulation apparatus consists in that the input apparatus, for example the mouse or the joystick, does not permit realistic simulation of the use of a surgical instrument, for example forceps.
It is therefore the object of the invention to specify a simulator apparatus of the type mentioned at the beginning that has a compact design and mechanics of low torque.
According to the invention, a simulator apparatus with at least two degrees of freedom of movement for an instrument that has an elongated shaft defining a longitudinal axis, is provided, said simulator apparatus comprising: a holding device for said instrument, said holding device being designed such that said instrument has at least a first degree of freedom of rotary movement about said longitudinal axis of said shaft and at least a second degree of freedom of translatory movement in the direction of said longitudinal axis of said shaft, said holding device having a gear arrangement for said first and second degrees of freedom, wherein said gear arrangement has a first bevel gear, which is connected to said shaft and corotates with the latter about said longitudinal axis thereof, and has a second and a third bevel gear which are arranged on either side of said first bevel gear and are in rolling engagement therewith.
The simulator apparatus according to the invention therefore has a gear arrangement that resembles a differential gear and has the advantage that it can be arranged around the shaft of the instrument and is of particularly small overall size, and in particular large radii of movement of the moving parts such as in the case of the known lever arrangements are avoided. Guiding of the instrument in the holding device with particularly low torque is thereby also achieved. Such a gear arrangement can be used both to implement the first degree of freedom of the rotary movement about the longitudinal axis of the shaft and the second degree of freedom of the translatory movement in the direction of the shaft with a force feedback as is additionally provided in a preferred refinement, and also a superimposition of the two movements is rendered possible with low torque by the gear arrangement provided according to the invention. Moreover, the gear arrangement with three bevel gears has the advantage that the actuators, for example electric motors, possibly present for a force feedback, can be arranged immovably in the simulator apparatus, the result being to avoid further moments of inertia and torques, and to avoid a greater space requirement for the movement of such motors.
In a preferred refinement, the first bevel gear is in rolling engagement with the shaft via one or more pinions with the aid of a tooth system extending along the shaft.
A transfer of a translatory movement of the shaft along its longitudinal axis onto the first bevel gear is effected with particularly low torque by means of this measure. In the case of such a longitudinal movement of the shaft, the first bevel gear is set rotating about its longitudinal axis, and this thereby sets the second and the third bevel gears in rotary movements of mutually opposite direction. Force feedback to the first degree of freedom can therefore be implemented with particular ease by providing the second and third bevel gears, which are retarded by one or more actuators, as in a further preferred refinement. In order to achieve force feedback to the degree of freedom of the translatory movement, the second and the third bevel gears are then driven in opposite directions with the same torque and at the same speed.
However, the same actuators can also be used to achieve force feedback to the degree of freedom of the rotary movement of the shaft about its longitudinal axis. Specifically, as already mentioned when the instrument is being rotated about its longitudinal axis the first bevel gear is also corotated about the longitudinal axis of the shaft and, in the process, this sets the second and the third bevel gears in rotary movements in the same direction. In order to achieve force feedback to the degree of freedom of the rotary movement of the shank about its longitudinal axis, the actuators must therefore retard the second and the third bevel gears in the same direction and with the same torque.
In a further preferred refinement, the second and the third bevel gears are arranged concentrically with the shaft.
This arrangement of the second and third bevel gears results in a particularly space saving design, of small overall size, of the gear arrangement and of the overall arrangement of shaft and gear arrangement.
In a further preferred refinement, the holding device further has a cardanic suspension such that the instrument has a third degree of freedom of a swiveling movement about a first swivel axis, and a fourth degree of freedom of a swiveling movement about a second swivel axis, running perpendicular to the first swivel axis.
In the case of real surgery, a surgical instrument can usually be swiveled about the plane of the body surface about two mutually perpendicular axes that intersect in the incision. With the previously mentioned refinement, the simulator apparatus according to the invention therefore also permits realistic simulation of such movements of an instrument. The simulator apparatus according to the invention therefore permits at least four degrees of freedom of movement for the instrument. A cardanic suspension has, moreover, the advantage of a compact design occupying little space such that this measure for the purpose of the object on which the invention is based constitutes a further contribution to achieving this object.
In a further preferred refinement, the cardanic suspension is formed by a bow-shaped element that can be swiveled about the first swivel axis, and an annular element that can swivel about the second swivel axis, the instrument being guided on the bow-shaped element.
This refinement implements a cardanic suspension that is of particularly simple design and has the further advantage that the gear arrangement provided according to the invention for the first and second degrees of freedom can be arranged in a space saving fashion in the arrangement composed of a bow-shaped element and the annular element. Moreover, in the case when these two degrees of freedom are provided with force feedback, as a result of this arrangement the corresponding actuators need not, in turn, also be moved.
In a further preferred refinement, there are fastened on the annular element two mutually opposite seats, arranged offset by approximately 90xc2x0 with reference to the second swivel axis, for a spherical element through which the shaft is passed through, the spherical element in the seats being held such that it can rotate relative to the seats about an axis of rotation passing through both seats, and such that it is immobile with reference to the seat perpendicular to this axis of rotation.
By means of this measure, in which the cardanic suspension has a spherical element for holding the instrument, the advantage is created that the spherical element forms a particularly space saving mechanical connection between the instrument and the bow-shaped element, forming the cardanic suspension, and the annular element. Moreover, the interior of the spherical element can be used for force feedback with particular effectiveness to hold the gear arrangement provided according to the invention, together with the actuators thereof.
Consequently, it is provided in a further preferred measure that the gear arrangement is arranged in the spherical element, a particularly space saving design of the entire simulator apparatus thereby being achieved despite the at least four possible degrees of freedom of movement of the instrument.
In a further preferred refinement, at least one actuator is provided in each case for the force feedback to the third and fourth degrees of freedom.
Owing to this measure, the third and the fourth degrees of freedom can also be simulated realistically with force feedback as it occurs in the case of a real handling of the instrument during an operation. It also holds, in turn, with regard to the motors provided for force feedback to the third and fourth degrees of freedom that these motors need not also be moved during the movement of the instrument in the simulator apparatus, and this is rendered possible by the cardanic suspension.
In a further preferred refinement, in each case one-position detection sensor is provided for determining the position of the instrument for at least one degree of freedom, preferably for all degrees of freedom.
The instantaneous values of all degrees of freedom of the instrument which are rendered possible by the simulator apparatus according to the invention can be detected in real time with the aid of such position detection sensors, and can be used, in turn, to generate signals for the force feedback in real time in a computer by appropriate signal processing.
In a further preferred refinement, the instrument has a moveable operating device, and the moveable operating device is equipped with force feedback.
Particularly when the instrument is not an endoscope, but a surgical instrument such as forceps or scissors, this measure has the advantage that the simulator apparatus according to the invention can also simulate the force resistances occurring during the real preparation, for example cutting or grasping, of tissue. In the simplest case, it is possible to attach to the moveable operating device a Bowden cable that is connected to an actuator which, in turn, receives control signals from the simulation computer system. With the refinement mentioned previously, the simulator apparatus according to the invention even has five degrees of freedom for the simulation.
In a preferred use of the simulator apparatus, the latter is used to simulate a minimally invasive operation on the human or animal body.
Further features and advantages emerge from the following description and the attached drawing.
It goes without saying that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or on their own, without departing from the scope of the present invention.